1. Field of the Invention
This invention relates to an image forming apparatus such as an electrophotographic apparatus for forming multicolor images (color images of two or more colors) or full color images and an image forming apparatus provided with a color recording and developing device constituting the output portion of a computer, a facsimile apparatus or the like.
2. Description of the Prior Art
As such an image forming apparatus, there is known, for example, a color electrophotographic copying apparatus for forming full color images. As the developing device in such copying apparatus, a plurality of developing devices containing developers of different colors therein are disposed relative to a latent image bearing member such as a photosensitive drum. On the other hand, as the arrangement and construction of the developing devices, there have heretofore been proposed an arrangement in which the plurality of developing devices are successively disposed along the peripheral surface of the latent image bearing member and an arrangement in which the plurality of developing devices are supported by a rotating body and by this rotating body being rotatively driven, only the developing device corresponding to the developer of a desired color is opposed to the latent image bearing member. In the case of the former, the plurality of developing devices are arranged along the peripheral surface of the latent image bearing member and therefore, the circumferential length of the latent image bearing member is necessarily long, which in turn leads to a disadvantage that the latent image bearing member becomes bulky. In contrast, in the case of the latter, one developing device is always opposed to the latent image bearing member and therefore, the circumferential length of the latent image bearing member can be minimized and accordingly, the latent image bearing member can be made compact. Thus, to make the image forming apparatus compact, it is effective to adopt the latter developing device.
However, in the rotational type developing device having a rotating body rotated while carrying such a plurality of developing devices thereon, a partial rotation moment acts on the rotating member unless all of the developing devices are carried at the developing device carrying positions on the rotating body. In such a case, a drive motor for rotatively driving the rotating body must have a great output sufficient to overcome the partial rotation moment and accordingly, the drive motor becomes great in capacity and expensive. Also, where a servo mechanism or the like is employed as control means for controlling the drive motor, there has been a problem that the control circuit of the drive motor becomes complicated due to the partial load of the drive motor.
Further, where the plurality of developing devices are carried on the rotating body, if each developing device is not mounted at a predetermined carrying position, there has been an undesirable possibility that the latent image on the latent image bearing member is developed by developer of a color different from a desired color.